Figure 52: Current Level (Amps) At Which Transient Faults Are Self-Extinguishing; Figure 53: Earth Fault In Petersen Coil Earthed System - GE MiCOM P40 Agile Technical Manual

P14x
below shows earth fault current levels, below which they self-extinguish on these types of system. Statistics
demonstrate that around 80% of earth faults in Petersen Coil earthed systems self-extinguish. This, in part,
explains their popularity.
140
120
100
80
60
40
20
V00756

Figure 52: Current level (amps) at which transient faults are self-extinguishing

The following figure depicts a simple network earthed through a Petersen Coil reactance. It can be shown that if
the reactor is correctly tuned, theoretically no earth fault current will flow.
Source
V
AN
jX
L
(=I )
I
L
f
Petersen
jX
L
Coil
V00631

Figure 53: Earth fault in Petersen Coil earthed system

Consider a radial distribution system earthed using a Petersen Coil with a phase to earth fault on phase C, shown
in the figure below:
P14xEd1-TM-EN-1
Earth fault extinction current limits
as per DIN VDE 0228 Part 2
0
11kV 22kV
Residual fault current—compensated neutral
Capacitive fault current—isolated neutral
-I
B
-I
C
V
AN
   
I I I
f B C
j X
L
V
 AN  
0 i f I I
B C
j X
L
Chapter 6 - Current Protection Functions
33kV 65kV
V V
AB ac
 
jX jX
C C
(=-I ) (=-I )
B C
-jX -jX -jX
C C C
110kV
-I
C
A
-I
B
V
AC
N
C
Current vectors for A phase fault
I
L
V
AB
B
125